Pseudo-plastic water based ink for ballpoint pen

ABSTRACT

A pseudo-plastic water based ink for a ballpoint pen comprising a colorant, water and 1 to 40% by weight of a polyglycerin fatty acid ester represented by the following Formula (I) and containing no water-soluble organic solvent:                    
     wherein R 1  to R 4  each represent independently an aliphatic acyl group having 12 to 20 carbon atoms or a hydrogen atom; R 5 ′s, which may be the same or different, represent an aliphatic acyl group having 12 to 20 carbon atoms or a hydrogen atom; n represents an integer of 1 to 30; and the total number of the aliphatic acyl groups is 1 to 5. 
     It is a pseudo-plastic water based ink for a ballpoint pen which has good aging stability and provides good writing feeling and which is excellent in cap-off resistance.

This application is a national phase application under 35 U.S.C. §371 ofInternational Application No. PCT/JP99/04740, filed Sep. 1, 1999, whichwas published in Japanese as International Publication No. WO 00/12638on Mar. 9, 2000 and claims the benefit of Japanese Patent ApplicationNo. 10/246763, filed Sep. 1, 1998.

TECHNICAL FIELD

The present invention relates to a water based ink for a ballpoint pen,more specifically to a shear thinning water based ink for a ballpointpen having advantages of a ballpoint pen using an oil based ink, thatis, a pseudo-plastic water based ink for a ballpoint pen.

BACKGROUND ART

In general, inks for a ballpoint pen have so far been classified into awater based ink for a ballpoint pen which contains a solvent comprisinga water based solvent such as water and has a low viscosity of 10 mPa·sor less and an oil based ink which contains a solvent comprising an oilbased solvent such as mineral oil, polyhydric alcohol, a fatty acid andcellosolve and has an ink viscosity of 1000 to 20000 mPa·s.

A ballpoint pen using an oil based ink for a ballpoint pen has suchstructure that the ink stuck on a ball through an ink reservoir having asmall diameter is transferred onto a paper surface by rotation of theball and only the transferred portion of the ink is fed again from thereservoir to the ball.

On the other hand, a ballpoint pen using a water based ink for aballpoint pen has such structure that the ink is fed to a ball surfaceand a paper surface by virtue of capillary action of a feed prepared bybinding fine fibers.

While the water based ink for a ballpoint pen and the oil based ink fora ballpoint pen described above each have excellent advantages, theyhave various problems as well.

For example, in the water based ink for a ballpoint pen, capillaryaction is used in a principle for feeding the ink because of a lowviscosity thereof, wherein a simple contact of the tip portion of theballpoint pen with paper allows the capillary action to be exerted onthe contact point thereof to feed the ink, and good lines can be writtenon a paper surface without applying so much writing pressure, so thatsplitting, starving and blobbing are not likely to take place. On theother hand, storing the ink directly in the ink reservoir allows the inkto leak due to vibration, impact and a rise in an external temperatureto make the amount of the ink to be fed to the ball instable, andtherefore the ballpoint pen requires a complicated structure having afeed prepared by binding fine fibers and has the problem that it isdifficult to observe the amount of the ink.

On the other hand, an oil based ink for a ballpoint pen is characterizedin that because of a high viscosity thereof, blobbing of the ink fromthe pen tip can be prevented and the ink can be stored directly in theink reservoir having a small diameter, so that the structure of theballpoint pen can be simplified and that the amount of the ink can beobserved by using a transparent material for the ink reservoir. On theother hand, there are involved the problems that since the ink istransferred only on a paper surface come into contact with the rotatingball, splitting and starving are liable to be caused if the ball rotatesunstably and that since the ink hardly penetrates into a paper surface,blobbing which causes stain with the untransferred ink is apt to becaused.

In recent years, in order to solve such problems, produced are waterbased inks for a ballpoint pen (hereinafter referred to as “apseudo-plastic water based ink for a ballpoint pen”) in which agelatinizer and a water soluble paste are added to a water-soluble inkto impart a specific viscosity characteristic to the ink.

A ballpoint pen using this pseudo-plastic water based ink for aballpoint pen is reduced in an ink viscosity by shear force which isapplied to the ink by rotation of the ball at the tip point when writingand can write as smoothly as a ballpoint pen using a water based ink tomake good lines on a paper surface. Further, when the pen is not usedfor writing, blobbing of the ink from the pen tip can be preventedbecause the ink has a high viscosity. The ink can be stored directly inthe ink reservoir, so that the structure thereof can be simplified, andthe use of a transparent material for the ink reservoir makes itpossible to observe the amount of the ink. Thus, the use of thepseudo-plastic water based ink for a ballpoint pen provides a-writinginstrument having both characteristics of a ballpoint pen using a waterbased ink and a ballpoint pen using an oil based ink.

When producing such a pseudo-plastic water based ink for a ballpointpen, a viscosity-controlling agent (thickener) has so far had to beblended as an essential component for an ink material. Theviscosity-controlling agent is added in order to impart apseudo-plasticity to the ink, and it is proposed to add, for example,polyacrylic acid salts, cross-linking type acrylic acid polymers, saltsof a styrene-acrylic acid copolymer, salts of a styrene-maleic acidcopolymer, nonionic polymers such as polyvinylpyrrolidone andpolyethylene glycol, and polysaccharides such as xanthan gum, guar gum,casein, gum arabic, gelatin, carrageenan, alginic acid, tragacanth gumand locust bean gum.

However, these viscosity-controlling agents have caused the problemsthat they bring about scattering in the capability for providing a shearthinning property depending on a lot to exert influence on the writingproperty and they are inferior in compatibility with some colorants tocause a change in a viscosity of the ink in heating and aging and reducethe performances of the ballpoint pen and that they restrict thecompounding of various materials such as a surfactant, an organicsolvent, a dispersing resin for a pigment and the like which arecompounded in addition to these viscosity-controlling agents into somekinds of the inks.

On the other hand, proposed in Japanese Patent Laid-Open No. Hei9-302299 is a shear thinning ink for a ballpoint pen which comprises acolorant, a water-soluble organic solvent and a nonionic surfactanthaving an HLB value of 8 to 12 as an agent for providing a shearthinning property and which has a viscosity of 25 to 160 mpa sdetermined at a revolution of 100 rpm by an EM type rotationalviscometer and a shear thinning index of 0.1 to 0.6.

However, all nonionic surfactants having an HLB alue of 8 to 12 do notalways impart the shear thinning property, and while-exhibiting theshear thinning property in an aqueous solution, a thickening property islost in many cases by blending a water-soluble organic solvent. Further,if a blending amount of the above surfactant is increased in order toimpart the shear thinning property and a water-soluble organic solventis blended into the system, feathering of the drawn lines is heavy tomake the lines very indistinct.

Further, proposed in U.S. Pat. No. 2,662,882 is a pigment ink for aballpoint pen which comprises a pigment, water, water-solublesaccharides and a polyglycerin fatty acid ester.

However, an ink using water-soluble saccharides as a main thickener isincreased in a concentration of the water-soluble saccharides(thickener) by a portion of moisture evaporated from the pen tip withthe passage of time, and a viscosity of the ink at the pen tip growslarge, which brings about the problems that the inferior flowability iscaused and the cap-off resistance is reduced.

The present invention has been made in light of the problems describedabove, and an object thereof is to provide a pseudo-plastic water basedink for a ballpoint pen which causes less scattering in a viscositydepending on a production lot and has satisfactory viscosity andpseudo-plasticity and which has good stability with the passage of timewhatever colorants are used and provides good writing feeling andexcellent cap-off resistance.

DISCLOSURE OF THE INVENTION

Intensive researches continued by the present inventors in order tosolve the problems described above have resulted in finding that apseudo-plastic water based ink for a ballpoint pen meeting the objectdescribed above can be obtained by adding a polyglycerin fatty acidester represented by Formula (I) and blending no water-soluble organicsolvent. Thus, the present invention has been completed.

That is, the pseudo-plastic water based ink for a ballpoint pen of thepresent invention is characterized by comprising a colorant, water and 1to 40% by weight of a polyglycerin fatty acid ester represented by thefollowing Formula (I) and containing no water-soluble organic solvent:

wherein R¹ to R⁴ each represent independently an aliphatic acyl grouphaving 12 to 20 carbon atoms or a hydrogen atom; R⁵′s, which may be thesame or different, represent an aliphatic acyl group having 12 to 20carbon atoms or a hydrogen atom; n represents an integer of 1 to 30; andthe total number of the aliphatic acyl groups is 1 to 5.

Further, the pseudo-plastic water based ink for a ballpoint pen has aviscosity of 100 to 4000 mPa·s at a shearing speed of 3.84 s5

Best Mode for Carrying Out the Invention

The embodiment of the present invention shall be explained below indetail.

The polyglycerin fatty acid ester added to the pseudo-plastic waterbased ink for a ballpoint pen of the present invention is represented byFormula (I) described above.

In Formula (I) described above, R¹ to R⁴ each represent independently analiphatic acyl group having 12 to 20 carbon atoms or a hydrogen atom;R⁵′s, which may be the same or different, represent an aliphatic acylgroup having 12 to 20 carbon atoms or a hydrogen atom; and n representsan integer of 1 to 30. The total number of the aliphatic acyl groups is1 to 5, preferably 1 to 3.

In Formula (I), the aliphatic acyl group having 12 to 20 carbon atomsrepresented by R¹ to R⁵ includes, for example, isostearoyl, oleoyl,stearoyl, palmitoyl and lauroyl.

Specific examples of the polyglycerin fatty acid ester represented byFormula (I) includes, for example, hexaglycerin isostearate,hexaglycerin stearate, hexaglycerin oleate, hexaglycerin palmitate,hexaglycerin laurate, hexaglycerin linoleate, hexaglycerin linolenate,hexaglycerin myristate, octaglycerin oleate, octaglycerin palmitate,octaglycerin laurate, octaglycerin linoleate, octaglycerin linolenate,octaglycerin myristate, decaglycerin oleate, decaglycerin palmitate,decaglycerin laurate, decaglycerin linoleate, decaglycerin linolenateand decaglycerin myristate. They may be used alone or in suitablecombination of two or more kinds thereof.

The polyglycerin fatty acid ester used in the present invention providesa good lubricating property, imparts a shear thinning property and has avaporization-controlling effect, and therefore it can be used as analternate material for each of a polar solvent, a lubricant and aviscosity-controlling agent in conventional materials. In particular,when it is used as an alternative for a viscosity-controlling agent, itis prevented that the scattering in the capability for providing a shearthinning property depending on a lot of the materials influences thewriting property and that a change in the viscosity in heating and agingis brought about because of inferior compatibility with a colorant toreduce a performance of the pen.

An addition amount of the polyglycerin fatty acid ester is suitablyselected from a range of 1 to 40% by weight, preferably 3 to 20% byweight based on the total amount of the pseudo-plastic water based inkfor a ballpoint pen.

The addition amount of less than 1% by weight does not provide asatisfactory thickening effect and brings about inconvenience such asblobbing of the ink from the pen tip. On the other hand, the additionamount exceeding 40% by weight raises a viscosity of the ink andtherefore is likely to bring about a reduction in the writing propertydue to inferior followability of the ink.

The pseudo-plastic water based ink for a ballpoint pen of the presentinvention is characterized by containing no organic solvent. If blendedwith the organic solvent, the satisfactory thickening effect is notobtained, and feathering of the drawn lines is heavy, so that the linesbecome very indistinct. Further, the pseudo-plastic water based ink fora ballpoint pen of the present invention is not blended with awater-soluble organic solvent such as ethylene glycol considering theenvironment.

Further, the polyglycerin fatty acid ester can be used, if necessary, incombination with other lubricants, viscosity-controlling agents and thelike respectively.

All dyes and pigments which can be dissolved or dispersed in water basedsolvents can be used as the colorant. Specific examples thereof includeacidic dyes such as Eosine, Phloxine, Water Yellow #6-C, acid red, WaterBlue #105, Brilliant Blue FCF and Nigrosine NB, direct dyes such asDirect Black 154, Direct Sky Blue 5B and Violet BB, basic dyes such asRhodamine and Methyl Violet, inorganic pigments such titanium dioxide,carbon black and ultramarine, organic pigments such as CopperPhthalocyanine Blue and Benzidine Yellow, and various metal powders.They each may be used alone or in suitable combination of two or morekinds thereof.

A use amount of the colorant is suitably selected from a range of 1 to40% by weight, preferably 3 to 20% by weight based on the total amountof the pseudo-plastic water based ink for a ballpoint pen.

When a pigment is used as the colorant, a water-soluble polymerdispersant and a surfactant may suitably be selected and blended.Specific examples thereof include anionic polymers such as polyacrylicacid salts, salts of a styrene-acrylic acid copolymer, salts of astyrene-maleic acid copolymer, salts of a vinylnaphthalene-maleic acidcopolymer and a β-naphthalenesulfonic acid-formalin condensationproduct, and nonionic polymers such as polyvinyl alcohol,polyvinylpyrrolidone and polyethylene glycol. A use amount thereof issuitably selected from a range in which the properties of thepseudo-plastic water based ink for a ballpoint of the present inventionpen are not damaged.

Components other than those described above may be added, if necessary,to the pseudo-plastic water based ink for a ballpoint pen of the presentinvention in a range in which the properties thereof are not damaged.The components which can be added include a lubricant such aspolyalkylene glycol derivatives, fatty acid alkali salts, nonionicsurfactants and fluorine base surfactants, a rust preventive such asbenzotriazole and saponins, a pH-controlling agent such as potassiumhydroxide and potassium phosphate, a preservative such as sodium omadineand 1,2-benzoisothiazoline, and a viscosity-controlling agent such aspolyacrylic acid salts and alginic acid.

A viscosity of the pseudo-plastic water based ink for a ballpoint pen ofthe present invention falls in a range of 100 to 4000 mPa·s, preferably200 to 2000 mPa·s and more preferably 300 to 1000 mPa·s at a shearingspeed of 3.84 s⁻¹.

If the viscosity of the ink is lower than 100 mPa·s, the ink is blobbedfrom the pen tip. Further, when a colorant having a large specificgravity such as titanium dioxide and metal powder is used, the viscosityhas to be controlled rather high in order to prevent the colorant fromsettling, and the upper limit thereof is preferably 4000 mPa·s. If theviscosity of the ink exceeds 4000 mPa·s, a reduction in the writingproperty due to inferior followability of the ink is apt to be broughtabout.

The pseudo-plastic (shear thinning) water based ink for a ballpoint penaccording to the present invention can easily be obtained by dissolvingthe components described above, if necessary, with heating and mixingthem under stirring.

EXAMPLES

The present invention shall be explained below in further details withreference to examples and comparative examples, but the presentinvention shall by no means be restricted by the examples.

Example 1

The following components were blended to obtain a blue pseudo-plasticwater based ink for a ballpoint pen:

Phthalocyanine blue 8.0% by weight Styrene-maleic acid resin 3.0% byweight ammonium salt Hexaglycerin isostearate 15.0% by weight  (1.5esters) Phosphoric acid ester 0.3% by weight 1,2-Benzoisothiazolone salt0.3% by weight (preservative) Aminomethylpropanol 0.3% by weight(pH-controlllng agent) Benzotriazole (rust preventive) 0.2% by weightIon-exchanged water balance

Example 2

The following components were blended to obtain a

Carbon black 7.0% by weight Styrene-acrylic acid resin 3.0% by weightammonium salt Octaglycerin oleate (2 esters) 5.0% by weight1,2-Benzoisothiazolone salt 0.3% by weight (preservative)Aminomethylpropanol 0.3% by weight (pH-controlling agent) Benzotriazole(rust preventive) 0.2% by weight Polyacrylic acid salt (acryl basesynthetic polymer: viscosity- 0.1% by weight controlling agent)Ion-exchanged water balance

Example 3

The following components were blended to obtain a blue pseudo-plasticwater based ink for a ballpoint pen:

Phthalocyanine blue 8.0% by weight Styrene-acrylic acid resin 2.7% byweight ammonium salt Decaglycerin palmitate (2 esters) 12.0% by weight 1,2-Benzoisothiazolone salt 0.3% by weight (preservative)Aminomethylpropanol 0.3% by weight (pH controlling agent) Benzotriazole(rust preventive) 0.2% by weight Polyacrylic acid salt (acryl basesynthetic polymer: viscosity- 0.1% by weight controlling agent)Ion-exchanged water balance

Comparative Example 1

A blue pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 1, except that 15% by weight ofpropylene glycol and 0.4% by weight of a cross-linking type acrylic acidpolymer were added respectively in place of hexaglycerin isostearate(1.5 esters).

Comparative Example 2

A blue pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 1, except that 15% by weight ofpropylene glycol was further added.

Comparative Example 3

A black pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 2, except that 3.0% by weight ofcarboxymethyl cellulose.(water-soluble polysaccharides) was added inplace of octaglycerin oleate (2 esters).

Comparative Example 4

A blue pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 3, except that 10% by weight ofpropylene glycol and 0.25% by weight of a polyacrylic acid salt wereadded respectively in place of decaglycerin palmitate (2 esters).

Comparative Example 5

A blue pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 3, except that 12% by weight of octanolethylene oxide 3 mole adduct (H. L. B.: 8.7) was added in place ofdecaglycerin palmitate (2 esters).

Comparative Example 6

A blue pseudo-plastic water based ink for a ballpoint pen was obtainedin the same manner as in Example 3, except that 20% by weight ofpropylene glycol and 0.80% by weight of a polyacrylic acid salt wereadded respectively in place of decaglycerin palmitate (2 esters).

Evaluation Tests

The pseudo-plastic water based inks for a ballpoint pen obtained inExamples 1 to 3 and Comparative Examples 1 to 6 were filled respectivelyinto a ballpoint pen having a ball diameter of 0.7 mm, and the ballpointpens thus obtained were used to carry out the evaluation tests of:

(1) an ink viscosity of the initial ink at a shearing speed of 3.84 s⁻¹,

(2) a change in the ink viscosity after stored at 50° C. for one month,

(3) time passed until starving is caused after left standing with thecap off,

(4) writing feeling of the pen,

(5) followability of the ink in the drawn lines obtained by writing witha hand,

(6) the presence of blobbing of the ink, and

(7) feathering in the drawn lines obtained by writing with a hand.

The results are shown in the following Table 1. The writing feeling (4),the ink followability (5) and the feathering (7) in the drawn lines wereevaluated respectively based on the following criteria.

Evaluation criteria of writing feeling:

∘: smooth and stable writing feeling

Δ: stiff and hard writing feeling

X: stiff and hard writing feeling with skipping and directivity

Evaluation Criteria of Ink Followability:

∘: capable of smoothly and stably writing

Δ: causing skipping in writing at a double speed

X: no follow-up of the ink to cause skipping in usual writing

Evaluation Criteria of Feathering in the Drawn Lines

∘: no feathering and distinct lines

Δ: feathering observed and indistinct lines

X: marked feathering observed and very indistinct lines

Comments on Table 1

As apparent from the results shown in Table 1, the pseudo-plastic waterbased inks for a ballpoint pen prepared in Examples 1 to 3 falling inthe scope of the present invention provided good results on all of anink viscosity, a viscosity change, time passed until starving is caused,writing feeling, ink followability, ink blobbing and feathering in thedrawn lines as compared with those of the pseudo-plastic water based inkfor a ballpoint pen prepared in Comparative Examples 1 to 6 fallingoutside the scope of the present invention. This makes it clear that thepseudo-plastic water based ink for a ballpoint pen of the presentinvention are apparently excellent.

TABLE 1 Example Comparative Example 1 2 3 1 2 3 4 5 6 (1) Ink viscosity550 550 450 700 300 600 500 30 4500 (mPa · s) (2) Viscosity change NoneNone None A little rise None Rise Down None Rise (3) Time until  28  21 21  28 days  28  14  14  60 One starving days days days days days daysdays day (4) Writing feeling ◯ ◯ ◯ Δ ◯ Δ ◯ ◯ X (5) Ink followability ◯ ◯◯ ◯ ◯ Δ ◯ ◯ X (6) Ink blobbing None None None None None None NonePresent None (7) Feathering in ◯ ◯ ◯ ◯ X ◯ ◯ X ◯ drawn lines

Industrial Applicability

According to the present invention, obtained is a pseudo-plastic waterbased ink for a ballpoint pen which has very good aging stability and isfree of feathering and which has a vaporization-inhibiting effect andprovides good writing feeling, and it can be applied to ballpoint penshaving the same structure as that of a ballpoint pen using an oil basedink.

What is claimed is:
 1. A pseudo-plastic water based ink for a ballpointpen comprising a colorant, water and 1 to 40% by weight of apolyglycerin fatty acid ester represented by the following Formula (I)and containing no water-soluble organic solvent:

wherein R¹ to R⁴ each represent independently an aliphatic acyl grouphaving 12 to 20 carbon atoms or a hydrogen atom; R⁵′s, which may be thesame or different, represent an aliphatic acyl group having 12 to 20carbon atoms or a hydrogen atom; n represents an integer of 1 to 30; andthe total number of the aliphatic acyl groups is 1 to
 5. 2. Thepseudo-plastic water based ink for a ballpoint pen as described in claim1, wherein the ink has a viscosity of 100 to 4000 mPa·s at a shearingspeed of 3.84 s⁻¹.